A number of methods and products have been developed to provide sustained release of active agents or drugs for their safe and effective administration to humans or animals. For example, sustained release of an active agent may allow a reduction in the daily dosing requirement and a more even and long-term absorption into the body of an individual. Enteric coatings on tablets, microencapsulation of active agents into microspheres, liposomes, etc., as well as the use of macromolecules, such as polypeptides, polysaccharides, etc., have been described previously. Direct covalent attachment of active agents to polypeptides as a way of providing sustained release has also been proposed. However, existing methods for synthesizing peptide-conjugated active agents are limited by their impractical reaction schemes that are generally not suitable for large-scale industrial, agricultural, or pharmaceutical applications. Therefore, a need exists in the art for improved methods of polypeptide or polymer synthesis having improved yield and efficiency that are further capable of incorporating active agents into a growing polypeptide chain.